eSpeak is a software speech synthesizer for English and other languages.
eSpeak produces good quality English speech. It uses a different synthesis
method from other open source TTS engines, and sounds quite different.
It's perhaps not as natural or "smooth", but some people may find the
articulation clearer and easier to listen to for long periods. eSpeak supports
several languages, however in most cases these are initial drafts and need more
work to improve them.
It can run as a command line program to speak text from a file or from stdin.